Turkish riot police use water cannons and tear gas to disperse protesters during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

Riot police use water cannons and teargas to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. The government deployed about 40,000 police officers in Istanbul and closed the main roads leading to Taksim Square.

A brass band from Britain's Rail, Maritime and Transport union takes part in a May Day Trades Unions workers' rights protest march in London, Thursday, May 1, 2014. This year's annual May Day protest had special emphasis on paying tribute to the lives of Bob Crow, the late general secretary of Britain's Rail, Maritime and Transport union and socialist politician Tony Benn who both died recently.

Photo: Matt Dunham, Associated Press

A brass band from Britain's Rail, Maritime and Transport union...

A brass band from Britain's Rail, Maritime and Transport union... Photo-6243642.84970 - SFGate

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WWII veterans take part in the May Day march in Simferopol, the Crimean capital on Thursday, May 1, 2014.

Photo: Max Vetrov, Associated Press

WWII veterans take part in the May Day march in Simferopol, the...

WWII veterans take part in the May Day march in Simferopol, the... Photo-6243683.84970 - SFGate

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Traditionally dressed dancers perform during the May Day celebrations in Lofer in the Austrian province of Salzburg, on Thursday, May 1, 2014.

Demonstrators wait for the start of a May Day Trades Unions workers' rights protest march in London, Thursday, May 1, 2014. This year's annual May Day protest had special emphasis on paying tribute to the lives of Bob Crow, the late general secretary of Britain's Rail, Maritime and Transport union and socialist politician Tony Benn who both died recently.

Photo: Matt Dunham, Associated Press

Demonstrators wait for the start of a May Day Trades Unions...

Demonstrators wait for the start of a May Day Trades Unions... Photo-6243647.84970 - SFGate

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Demonstrators gather for a rally in Trafalgar Square during a May Day Trades Unions workers' rights protest march in London, Thursday, May 1, 2014. This year's annual May Day protest had special emphasis on paying tribute to the lives of Bob Crow, the late general secretary of Britain's Rail, Maritime and Transport union and socialist politician Tony Benn who both died recently.

Photo: Matt Dunham, Associated Press

Demonstrators gather for a rally in Trafalgar Square during a May...

Demonstrators gather for a rally in Trafalgar Square during a May... Photo-6243649.84970 - SFGate

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Demonstrators march in May Day protests in the Northern Greek city of Thessaloniki on Thursday, May 1, 2014. Thousand protesters attended in three separate peaceful rallies in Thessaloniki, with demonstrations aimed at ongoing austerity measures in the crisis-hit country, that have caused a dramatic rise in poverty and unemployment.

Photo: Nikolas Giakoumidis, Associated Press

Demonstrators march in May Day protests in the Northern Greek city...

Demonstrators march in May Day protests in the Northern Greek city... Photo-6243653.84970 - SFGate

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Members of pro-communist union PAME gather in May Day protests in the Northern Greek city of Thessaloniki on Thursday, May 1, 2014. Thousand of protesters attended in three separate peaceful rallies in Thessaloniki, with demonstrations aimed at ongoing austerity measures in the crisis-hit country, that have caused a dramatic rise in poverty and unemployment.

Photo: Nikolas Giakoumidis, Associated Press

Members of pro-communist union PAME gather in May Day protests in...

Members of pro-communist union PAME gather in May Day protests in... Photo-6243651.84970 - SFGate

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Paco Fiallo, 39 years old, right, makes a balloon on the street with his face painted as a clown during May Day, in Pamplona, northern Spain, Thursday, May 1, 2014. Tens of thousands of workers marked May Day in European cities with a mix of anger and gloom over austerity measures imposed by leaders trying to contain the eurozone's intractable debt crisis.

Workers march on the street holding a banner which reads: ''For the distribution the work and wealth'', during May Day, in Pamplona northern Spain, Thursday, May 1, 2014. Tens of thousands of workers marked May Day in European cities with a mix of anger and gloom over austerity measures imposed by leaders trying to contain the eurozone's intractable debt crisis.

Photo: Alvaro Barrientos, Associated Press

Workers march on the street holding a banner which reads: ''For...

Workers march on the street holding a banner which reads:... Photo-6243656.84970 - SFGate

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A member of Sri Lanka's Marxist Party Peoples Liberation Front shouts slogans against the Sri Lankan government during a parade held to mark the International Labor Day or May Day in Colombo, Sri Lanka, Thursday, May 1, 2014.

Photo: Eranga Jayawardena, Associated Press

A member of Sri Lanka's Marxist Party Peoples Liberation Front...

A member of Sri Lanka's Marxist Party Peoples Liberation Front... Photo-6243659.84970 - SFGate

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A member of Sri Lanka's Marxist Party Peoples Liberation Front carries a flag symbolizing the working class during a parade held to mark the International Labor Day or May Day in Colombo, Sri Lanka, Thursday, May 1, 2014.

Photo: Eranga Jayawardena, Associated Press

A member of Sri Lanka's Marxist Party Peoples Liberation Front...

A member of Sri Lanka's Marxist Party Peoples Liberation Front... Photo-6243658.84970 - SFGate

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Anti-Nazi activists taunt supporters of the far-right NPD political party marching on May Day in Dierkow district on May 1, 2014 in Rostock, Germany. Left-wing protesters repeatedly blocked the route of the approximately 250 NPD supporters and at one point attacked them with rocks. May Day gatherings and protests are taking place across Germany today and the one in Rostock was the NPD's main march.

A protester stands as riot police use water cannons and teargas to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

Photo: Emrah Gurel, Associated Press

A protester stands as riot police use water cannons and teargas to...

A protester stands as riot police use water cannons and teargas to... Photo-6243661.84970 - SFGate

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A protester fires toward riot police in Istanbul, Turkey, Thursday May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

Turkish riot police use water cannons and tear gas to disperse protesters during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

People hold candles as they pray for the safe return of missing passengers and tribute to the victims of the sunken ferry Sewol on May 1, 2014 in Seoul, South Korea. No survivors have been found since 174 passengers and crew were rescued on the day of the incident, April 16. South Korea's trade union, the Federation of Korean Trade Unions (FKTU) had announced cancellation of its annual May Day rally to mourn the ferry disaster victims.

Photo: Chung Sung-Jun, Getty Images

People hold candles as they pray for the safe return of missing...

People hold candles as they pray for the safe return of missing... Photo-6243665.84970 - SFGate

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A protester uses a slingshot toward riot police in Istanbul, Turkey, Thursday May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

A protester throws a teargas canister toward riot police who use water cannons and teargas to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

Turkish riot police use water cannons and tear gas to disperse protesters during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

A protester takes aim at riot police with a slingshot during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

Photo: Burak Kara, Getty Images

A protester takes aim at riot police with a slingshot during a May...

A protester takes aim at riot police with a slingshot during a May... Photo-6243671.84970 - SFGate

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A protester uses a slingshot toward riot police who use water cannons and teargas to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

A protester takes aim at riot police with a slingshot and a flare gun during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

Photo: Burak Kara, Getty Images

A protester takes aim at riot police with a slingshot and a flare...

A protester takes aim at riot police with a slingshot and a flare... Photo-6243669.84970 - SFGate

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Members of workers' unions attend a May Day protest in Belgrade, Serbia, Thursday, May 1, 2014. Various labor groups staged a protest in Belgrade in order to voice their concern over the expected austerity measures announced by Serbia's new government.

Photo: Marko Drobnjakovic, Associated Press

Members of workers' unions attend a May Day protest in Belgrade,...

Members of workers' unions attend a May Day protest in... Photo-6243672.84970 - SFGate

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Riot police use water cannon vehicles to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square.

Protesters shout slogans and hold banners during a May Day demonstration on May 1, 2014 in Macau, China. Hundreds of protesters attended a march against job shortages and living conditions on May Day.

Photo: Lam Yik Fei, Getty Images

Protesters shout slogans and hold banners during a May Day...

Protesters shout slogans and hold banners during a May Day... Photo-6243678.84970 - SFGate

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A protester shouts slogans as he stands on top of a van during a May Day demonstration on May 1, 2014 in Macau, China. Hundreds of protesters attended a march against job shortages and living conditions on May Day.

Photo: Lam Yik Fei, Getty Images

A protester shouts slogans as he stands on top of a van during a...

A protester shouts slogans as he stands on top of a van during a... Photo-6243676.84970 - SFGate

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A woman sits on the fringes of a May Day protest in Belgrade, Serbia, Thursday, May 1, 2014. Various labor groups staged a protest in Belgrade in order to voice their concern over the expected austerity measures announced by Serbia's new government.

Photo: Marko Drobnjakovic, Associated Press

A woman sits on the fringes of a May Day protest in Belgrade,...

A woman sits on the fringes of a May Day protest in Belgrade,... Photo-6243679.84970 - SFGate

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DGB union official Werner Klump attends a meeting at the Brandenburg Gate after marching through the city center on May 1, 2014 in Berlin, Germany. May Day, the international day of labour, is a national holiday in Germany and observed with gatherings by labour unions and political parties. In some cities, including Hamburg and Berlin, the day often ends with violent clashes between police and mostly left-wing demonstrators.

A masked dancer somersaults as he performs during a May Day rally in Jakarta, Indonesia, Thursday, May 1, 2014.

Photo: Dita Alangkara, Associated Press

A masked dancer somersaults as he performs during a May Day rally...

A masked dancer somersaults as he performs during a May Day rally... Photo-6243689.84970 - SFGate

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Bangladeshi workers unload sand and gravel used for construction purpose from a ferry at the Buriganga River on the eve of May Day in Dhaka, Bangladesh, Wednesday, April 30, 2014. The workers earn less than US$ 3 a day.

Protesters shout slogans and hold banners during a May Day demonstration on May 1, 2014 in Macau, China. Hundreds of protesters attended a march against job shortages and living conditions on May Day.

Photo: Lam Yik Fei, Getty Images

Protesters shout slogans and hold banners during a May Day...

Protesters shout slogans and hold banners during a May Day... Photo-6243682.84970 - SFGate

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A protester uses a slingshot toward riot police in Istanbul, Turkey, Thursday May 1, 2014. Clashes erupted between May Day demonstrators and riot police as crowds determined to defy a government ban tried to march to the city's iconic Taksim Square. Security forces pushed back demonstrators with water cannons and tear gas.

Turkish riot police use water cannons and tear gas to disperse protesters during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.

Riot police use water cannons and teargas to disperse thousands of people trying to reach the city's main Taksim Square to celebrate May Day in Istanbul, Turkey, Thursday, May 1, 2014. The government deployed about 40.000 police officers in Istanbul and closed the main roads leading to Taksim Square.

Turkish riot police use water cannons and tear gas to disperse protesters during a May Day demonstration on May 1, 2014 in Istanbul, Turkey. Turkish police fired water cannon and tear gas on Thursday in an attempt to prevent hundreds of protesters from defying a ban on May Day rallies and reaching Istanbul's central Taksim Square, the focal point of protests last summer.